CLONING FROM PURIFIED HIGH ENDOTHELIAL VENULE CELLS OF HEVIN, A CLOSERELATIVE OF THE ANTIADHESIVE EXTRACELLULAR-MATRIX PROTEIN SPARC

High endothelial venules (HEV) in lymphoid tissues support high levels of lymphocyte extravasion from the blood. We purified high endothelia l cells from human tonsils by immunomagnetic selection with MECA-79 MA b to construct an HEV cDNA library. Differential screening of this lib rary using cDNA probes from HEV (plus) or flat-walled vessel (minus) e ndothelial cells allowed us to characterize a novel human cDNA express ed to high levels in HEV. The cDNA encodes a secreted acidic calcium-b inding glycoprotein of 664 aa residues, designated hevin, exhibiting 6 2% identify with the antiadhesive extracellular matrix protein SPARC, over a region of 232 aa spanning more than four fifths of the SPARC co ding sequence. The primary structure and sequence of hevin are similar to SPARC-like proteins from rat and quail, called SC1 or QR1. Hevin c ould contribute to the induction or maintenance of features of the HEV endothelium that facilitate lymphocyte migration.